The present invention relates to medical equipment and more particularly to an apparatus for bone fixation allowing the movement of bones at a broken joint.
For the purposes of this invention, such a fixation is termed a "dynamic fixation". This designates a bone fixation, by means of pins, bars and external supports, which has an articulation in geometrical relationship with an articulation of the human or animal body, allowing the fixation of bone fragments of each one of the bones which are articulated, but allowing also a pivoting movement of the parts of the fixation device about their axis of articulation.
External anchoring or fixing of bones is an old surgical technique which was first used a century ago. Its application has for a long time been limited to complicated fractures in traumatology and consequently in orthopedics, i.e. the secondary treatment of fractures, infections, slow knitting of the bones, pseudarthroses, difficult bone-settings, etc. External anchoring is used particularly for long bones such as the femur, the tibia, the humerus, the radius and the cubitus. However, it is also desirable to manufacture small anchoring means which can be used on small bones, such as the metatarsals and the metacarpals, and in maxillofacial surgery as well as in experimental surgery on small animals.
External bone-anchoring elements enable two kinds of bone-anchoring to be carried out:
transfixing anchoring, wherein the pins extend from one side of the limb to the other, and
non-transfixing anchoring, wherein the pins are introduced into the bone without completely transversing it.
Transfixing anchorage, which is mostly used on the leg, is more rigid than non-transfixing anchorage. At both sides of the bone are fitted two rods or frames, upon which are anchored two groups of pins disposed on either side of the fracture. The two frames or the two rods are interconnected by a brace which is as stable as possible and which may comprise sliding rods or bars, the length of which can be increased or reduced.
Thus the basic techniques of external bone fixation are already known. Consideration has already been given to extending external bone fixation to the osteosynthesis of broken joints. This idea was to fix the bone fragments of the broken joint parts to the adjacent bones by means of thin pins, to introduce fixation pins into the other member of the joint (which may also be broken or not) also, and to join these two parts of the external fixation device by an articulation coupling. The purpose of this articulated fixation is the following. Normally, a rigid bone fixation would be a sufficient means for curing the broken bone. However, when this broken bone is part of a joint, there is a great risk that the joint will remain stiff after healing, and it is considered as absolutely necessary that the patient make movement exercises with his broken joint as soon as possible. Such movements should begin with a small angle of flexion which will gradually be increased. All these movements must of course be permitted by the mounted external fixation device, and that is not the case with the rigid fixation device described, for example, in U.S. Pat. No. 4,365,624.
A dynamic external fixation device has been described in the French Patent Application No. 2,551,650 published March 15, 1985, of Terry A. Clyburn. This fixation device comprises, following the general idea mentioned above, a first proximal branch and a second distal branch, these branches being adapted for fixably receiving fixation pins, and a universal joint, typically a ball joint, linking said two branches.
In order to function correctly, the fixation device must of course be applied strictly in such a manner that the point of articulation between said branches of the device will lie exactly on the pivot axis of the wrist joint; otherwise, undue and painful tensions or compressions occur when the hand is to be moved with respect to the arm. However, this axis of articulation in the joints is in most cases not detectable with sufficient precision when there is a fresh fracture, all of the area being swollen and the joint not being pivotable. Furthermore, the location of the articulation point of this known device cannot be adjusted.